An M-class dwarf star called GJ 667C, which is 22 light-years away from Earth, had previously been observed to have a super-Earth (called GJ 667Cb) that orbited the star in only 7.2 days, making it too close to the star, and thus too hot, to support life.

The study started with the aim of learning more about the orbit of GJ 667Cb. But the research team found a clear signal of a new planet (GJ 667Cc) with an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth.

Though the planet is much closer to its star than the Earth, the star itself is much smaller and dimmer, so overall the planet gets about the same amount of energy as the Earth.

Billions and billions! Astronomers have concluded that the stars in the Milky Way must average at least one planet per star. More importantly, the data says the galaxy should have billions of habitable planets.

[According to astronomer Uffe Gråe Jørgensen], a statistical analysis … shows that out of the Milky Way’s 100 billion stars, there are about 10 billion stars with planets in the habitable zone. This means that there may be billions of habitable planets in the Milky Way.

Want to read the actual paper, “A Sun-like star with three sub-Neptune exoplanets and two Earth-size candidates,” describing the discovery announced yesterday of two Earth-sized planet? You can download it here.

The paper’s closing paragraph sums the discovery up nicely:

A striking feature of the Kepler-20 planetary system is the presence of Earth-size rocky planet candidates interspersed between volatile-rich sub-Neptunes at smaller and larger orbital semi-major axes, as also seen in Kepler candidate multi-planet systems. Assuming that both [Kepler-20e] and [Kepler-20f] are planets, the distribution of the Kepler-20 planets in orbital order is as follows: Kepler-20b (3.7 days, 1.9 Earth radii), [Kepler-20e] (6.1 days, 0.9 Earth radii), Kepler-20c (10.9 days, 3.1 Earth radii), [Kepler-20f] (19.6 days, 1.0 Earth radii), and Kepler-20d (77.6 days, 2.8 Earth radii). Given the radii and irradiation fluxes of the two Earth-size planet candidates, they would not retain gas envelopes. The first, second, and fourth planets have high densities indicative of solid planets, while the other two planets have low densities requiring significant volatile content. The volatile-rich third planet, Kepler-20c dominates the inner part of the Kepler-20 system, by holding much more mass than the other three inner planets put together. In the Solar System, the terrestrial planets, gas-giants, and ice giants are neatly segregated in regions with increasing distance from the sun. Planet formation theories were developed to retrodict these Solar System composition trends. In the Kepler-20 system, the locations of the low-density sub-Neptunes that are rich in water and/or gas, and the Earth-size planet candidates does not exhibit a clean ordering with orbital period, challenging the conventional planet formation paradigm. In situ assembly may form multi-planet systems with close-in hot-Neptunes and super-Earths, provided the initial protoplanetary disk contained massive amounts of solids (∼ 50–100 Earth masses) within 1AU of the star.

The plethora of new exoplanet discoveries has astronomers longing for a telescope that can see them up close.

Astronomers need either a giant space telescope equipped with a device for blocking starlight, or an interferometer, consisting of several telescopes flying in formation. NASA did develop a proposal for such a space telescope, called Terrestrial Planet Finder, and the European Space Agency hoped to fly a similar mission called Darwin. But budgetary constraints have left both missions in limbo, unlikely to advance to the front of either agency’s queue until well into the next decade. At the conference, Traub raised the issue. “People are not thinking deeply about the distant future. People are wrapped up with what they’re doing right now,” he says. “Clearly, I’m concerned.”

The uncertainty of science: The discoverers of the possibly habitable exoplanet Gliese 581g defend their work against recent science attacks.

Exoplanets galore! The Kepler team announced today the discovery of 68 Earth-sized planets, five in the habitable zone. Key quote:

The discoveries are part of several hundred new planet candidates identified in new Kepler mission science data, released on Tuesday, Feb. 1. The findings increase the number of planet candidates identified by Kepler to-date to 1,235. Of these, 68 are approximately Earth-size; 288 are super-Earth-size; 662 are Neptune-size; 165 are the size of Jupiter and 19 are larger than Jupiter. Of the 54 new planet candidates found in the habitable zone, five are near Earth-sized. The remaining 49 habitable zone candidates range from super-Earth size — up to twice the size of Earth — to larger than Jupiter.

The NASA Kepler Mission has discovered over 700 candidate planets, with most having diameters less than 5 times that of Earth and some as small as that of Earth. One planet has a radius, mass, and density in a new domain having no counterpart in our Solar System, opening a new chapter in planetary science. [emphasis mine]

A press conference is scheduled for 11 am (Eastern). Stay tuned!

Update I. A NASA press release just made public says that Kepler has discovered a rocky planet only 1.4 times the size of the Earth.

Kepler 10b [is] a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter — similar to that of an iron dumbbell.

The press conference is ongoing, but the Kepler results are still to come.

Update II. The star the planet orbits, Kepler 10, is similar to our Sun in mass and size, but older, about 8 billion years old, and is 560 light years away. Kepler 10 is also a relatively bright star in the Kepler field of view, about 11 magnitude.

The planet’s orbit itself is only 8.4 days long. Its density, 8.8 grams per cubic centimeter, is 8.8 times greater than Earth’s. This data, based on all planet models, also suggests that the planet should be a rocky planet like the Earth, though heavier and larger with a surface gravity twice that of Earth.

Since the planet orbits so close to its sun, it is a scorched world, very hot. The scientists expect that it has no atmosphere. It is also probably tidally locked, with one side always facing its Sun.

Update III: Geoffrey Marcy, one of the world’s premier exoplanet scientists, is now commenting on these Kepler results, saying he considers this discovery “among the most profound discoveries in human history.”

Update IV: In answer to a press question, the scientists speculated that the planet might have formed as a gas giant farther from the star, then migrated inward and had its gas atmosphere stripped away. No one knows yet if this is true however.

Studies of further transits might learn more about the planet, such as the temperatures between its two hemispheres. As the planet orbits the star and its illuminated side comes into view, they can see the change in temperature and thus track it. Right now they think the sunlight side could be as hot as 2500 degrees Fahrenheit.

If you want to watch the press conference for yourself, they will be posting the video here.

Big news! Scientists have discovered the first rocky terrestrial planet orbiting its sun at a distance where life as we know it could form. The planet itself has a mass three to four times Earth, so no matter what, conditions on its surface would be very different than here. Nonetheless, this is a major discovery, and is only the first of many. Key quote:

The discovery suggests habitable planets must be common, with 10 to 20 per cent of red dwarfs and sun-like stars boasting them, the team says. That’s because Gliese 581 is one of just nine stars out to its distance that have been searched with high enough precision to reveal a planet in the habitable zone.

Don’t bet the bank on this: In a preprint paper posted tonight on the astro-ph website, scientists predict the discovery of the first Earthlike extrasolar planet — using statistical analysis alone! Fun quote:

Using a bootstrap analysis of currently discovered exoplanets, we predict the discovery of the first Earth-like planet to be announced in the first half of 2011, with the likeliest date being early May 2011.

The mapping of the atmospheres and surfaces of some extrasolar planets, even at distances of many light years, is now possible.

In its first six weeks of observation, the Kepler mission apparently found almost 150 planets similar in size to the Earth. The results, learned by accident because a talk given by one of the co-investigators was posted on the web, have not yet been officially announced because the project scientists feel a need for additional time to confirm them. Many of these so-called planets might turn out to be false positives, so some caution is in order.

The birth of extrasolar helioseismology: Using the first month of data from Kepler, scientists have actually detected oscillations or fluctuations in the shapes of 47 red giants (the equivalent of stellar earthquakes). The pdf preprint is here.

“Not simply about one mission, [Genesis] is also the history of America’s quest for the moon… Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America’s greatest human triumphs.” –San Antonio Express-News